The present invention relates to a hydraulic actuating device for a closure assembly. The present invention also relates to a closure assembly provided with an hydraulic actuating device, and a vehicle provided with a bodywork and a closure element for closing off an opening in the bodywork provided with an hydraulic actuator.
Various hydraulically actuated closure assemblies are known from the prior art. By way of example, reference is here made to DE 196 41 428, EP 0 803 630 and NL 1011362.
In these known closure assemblies, various solutions are proposed with regard to the risk of an object or body part becoming jammed as the closure element is closed and the risk of a motion of the closure element being obstructed, for example because the closure element, as it is opened, collides with something.
Especially with regard to the jamming of a body part, there is the requirement not only for the maximum force which can be delivered by the actuator to be heavily reduced during the last part of the closing motion and/or for the closing motion to be halted, but also for the motion of the closure element to be reversed so that the jammed body part is freed. The known hydraulically actuated closure assemblies do not provide any such automatic reversal.
The invention sets out to provide a hydraulic operating device for a closure assembly by which the above-stated object can be achieved, which actuating device is simply constructed and highly reliable.
The invention provides a hydraulic actuating device for a closure assembly, which is characterized in that a hydraulic flow sensor connected to the control means is provided at each pressure-limit valve, such that the one or more hydraulic flow sensors detect the presence of a flow of hydraulic fluid through the pressure-limit valve to the reservoir, and in that the control means are set upxe2x80x94if a flow sensor detects a flow of hydraulic fluidxe2x80x94to reverse the supply of hydraulic fluid under pressure to the actuator, so that the opening motion is changed to a closing motion or vice versa.
The invention envisages that the exceeding of the permitted pressure value in the opening chamber or the closing chamber, which pressure value is set by a pressure-limit valve, leads to the opening of the pressure-limit valve in question and the discharge of fluid to the reservoir. By detecting this discharge by means of a hydraulic flow sensor, the control means establish that the maximum limit value for the pressure has been exceeded. The control means then react by reversing the direction of motion of the actuator.
The flow sensor can be realized in various ways, but is preferably of an embodiment as described in NL 1014476 of the applicant is provided.
Preferably, it is envisaged that a single hydraulic flow sensor common to all pressure-limit valves is provided, which detects the presence of a flow from each of the pressure-limit valves to the reservoir.
Preferably, the hydraulic flow sensor form a free passage for the fluid through the reservoir line, so that the limitation of the pressure in the opening chamber and closing chamber by an associated pressure-limit valve is always operative. In the event of failure of the flow sensor or the control means, only the intended reversal of the direction of motion would then remain undone.
The solution according to the invention is considerably more advantageous than the use of costly electrical pressure sensors for measuring the pressure in the opening chamber and the closing chamber. Moreover, the control means are less complex than in combination with pressure sensors.
In a simple variant, the first and second pressure-limit valves connect to a common reservoir line to the reservoir and the hydraulic flow sensor is installed in the common reservoir line. The limit values for the pressures which lead to the opening of the various pressure-limit valves are, in practice, advantageously varied.
In a preferred embodiment, it is envisaged that the actuator has a by-pass connection, which, at a by-pass mouth, connects to the cylinder space, which by-pass mouth lies between the connecting mouths of the opening chamber and the closing chamber. A third pressure-limit valve is further provided, which connects to the by-pass connection, so that, in a first range of the closing motion, the closing chamber is only connected to the associated connection and is closed off from the by-pass connection, and so that, in a second range, the closing chamber is connected both to the associated connection and to the by-pass connection.
By realizing the third pressure-limit valve such that this valve opens at a lower pressure than the second pressure-limit valve, it is achieved that in the second range of the closing motion the force which can be delivered by the actuator is less than in the first range.
In a practical embodiment of the variant described above, it is envisaged that the first, second and third pressure-limit valves connect to a common reservoir line to the reservoir and that the hydraulic flow sensor is installed at this common reservoir line.
This solution gives rise to the effect that, in a first range of the opening motion, the force which can be delivered by the actuator is determined by the first pressure-limit valve and, in a second range, by the third pressure-limit valve. If the third-pressure limit valve opens at a lower pressure value, the force which can be delivered by the actuator in the second range of the opening motion is thus less than in the first range. Depending on the further embodiment of the closure assembly, this can be acceptable. If this reduction is undesirable or inadmissible, the invention proposes a further, more complex embodiment.
In this more complex embodiment, it is envisaged that the second and third pressure-limit valves as well as the connection of the opening chamber connect, via a non-return valve closing in the direction of the opening chamber, to a common reservoir line, in which the hydraulic flow sensor and, between the flow sensor and the reservoir, the first pressure-limit valve are accommodated, the common line between the flow sensor and the first pressure-limit valve connecting, via a non-return valve closing in the direction of the reservoir line, to the opening chamber. By this embodiment it is achieved that the pressure in the opening chamber is only limited by the first pressure-limit valve, even when the mouth of the by-pass connection is connected to the opening chamber. During closure, the by-pass connection, together with the associated third pressure-limit valve, is operative. This effect can also be achieved, though, with other hydraulic circuits.
The invention as well as advantageous embodiments thereof will be explained in greater detail below with reference to the drawing.